C++ Vector 内存分配

vector会预先分配比当前数据大的一个空间，如果有新的元素进来填满了这个空间，就又会继续分配。

分配策略一般是1，2，4，8，16...

直接上代码：

#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <math.h>
#include <list>
#include <string>

using namespace std;

class Point
{
public:
    Point()
    {
        cout << "construction" << endl;
    }
    Point(const Point& p)
    {
        cout << "copy construction" << endl;
    }
    ~Point()
    {
        cout << "destruction" << endl;
    }
};

int main(int argc, const char * argv[])
{
    Point test[10];
    cout << "**************************" << endl;
    vector<Point> arr;
    for (int i = 0; i < 10; i++)
    {
        arr.push_back(test[i]);
        cout << "capacity=" << arr.capacity() << ",size=" << arr.size() << endl;
        cout << "--------------------------" << endl;
    }
    return 0;
}

结果：

construction

construction

construction

construction

construction

construction

construction

construction

construction

construction

**************************

copy construction

capacity=1,size=1

--------------------------

copy construction

copy construction

destruction

capacity=2,size=2

--------------------------

copy construction

copy construction

copy construction

destruction

destruction

capacity=4,size=3

--------------------------

copy construction

capacity=4,size=4

--------------------------

copy construction

copy construction

copy construction

copy construction

copy construction

destruction

destruction

destruction

destruction

capacity=8,size=5

--------------------------

copy construction

capacity=8,size=6

--------------------------

copy construction

capacity=8,size=7

--------------------------

copy construction

capacity=8,size=8

--------------------------

copy construction

copy construction

copy construction

copy construction

copy construction

copy construction

copy construction

copy construction

copy construction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

capacity=16,size=9

--------------------------

copy construction

capacity=16,size=10

--------------------------

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction

destruction